Method and appratus for detecting undesirable rotation of medical markers

Abstract

Provided is a data processing method for determining rotation by a marker device of a medical tracking system about its mount. The data processing method includes acquiring a first marker device position dataset which represents a position of the marker device before a movement of the marker device. A second marker device position dataset is acquired which represents the position of the marker device after a movement of the marker device. A marker device displacement dataset is calculated, which represents the displacement of the marker device, from the first and second marker device position datasets. At least one axis of rotation of the marker device displacement dataset is calculated. A determination is made whether or not the marker device is rotated about its mount from the position of the at least one axis of rotation relative to the marker device.

It is claimed: 
     
         1 . A data processing method for determining rotation by a marker device of a medical tracking system about its mount, comprising:
 acquiring, by a tracking device, a first marker device position dataset that represents a position of the marker device before a movement of the marker device;   acquiring, by the tracking device, a second marker device position dataset that represents the position of the marker device after the movement of the marker device;   calculating, by a computer operably associated with the tracking device, a marker device displacement dataset from the first and the second marker device position datasets, the marker device displacement dataset representing the displacement of the marker device;   calculating, by the computer, at least one axis of rotation of the marker device displacement dataset, the calculated at least one axis of rotation including a position of the at least one axis of rotation;   determining, by the computer, whether or not the marker device is rotated about its mount based on the position of the at least one axis of rotation relative to the marker device; and   outputting indication information to an associated user when the computer has determined that the marker device has rotated about its mount, the indication information informing the associated user that the marker device has rotated about its mount.   
     
     
         2 . The method according to  claim 1 , wherein the first and the second marker device position datasets are marker device position matrices, and the marker device displacement dataset is a marker device displacement matrix. 
     
     
         3 . The method according to  claim 2 , further comprising:
 calculating Euler angles of the marker device displacement matrix; and   calculating the at least one axis of rotation and determining whether or not the marker device is rotated about its mount only if at least one of the Euler angles is larger than a predetermined minimum angle threshold.   
     
     
         4 . The method according to  claim 2 , wherein the at least one axis of rotation is calculated as an eigenvector of the marker device displacement matrix. 
     
     
         5 . The method according to  claim 4 , wherein only one axis of rotation corresponding to the eigenvector with a largest eigenvalue is determined. 
     
     
         6 . The method according to  claim 2 , wherein the marker device displacement matrix is calculated as a product of an inverse of the second marker device position matrix and the first marker device position matrix. 
     
     
         7 . The method according to  claim 1 , wherein the marker device is determined to have rotated about its mount if a distance between an axis of rotation and a point defined relative to the marker device is below a predetermined maximum distance threshold. 
     
     
         8 . The method according to  claim 7 , further comprising:
 acquiring a mechanical axis indication information dataset that represents information on a position of a mechanical axis of the mount; and   adjusting the maximum distance threshold in accordance with the mechanical axis indication information dataset.   
     
     
         9 . The method according to  claim 1 , wherein the marker device is determined to have rotated about its mount if a difference between a determined axis of rotation and a mechanical axis of the mount is below a predetermined axis deviation threshold. 
     
     
         10 . The method according to  claim 1 , wherein a marker device position dataset is acquired by acquiring a plurality of sample marker device position datasets, averaging the plurality of sample marker device position datasets and using the average as the marker device position dataset if a standard deviation of the sample marker device position datasets is below a predetermined position threshold. 
     
     
         11 . The method according to  claim 1 , wherein a marker device position dataset is acquired by sampling, for each marker of the marker device, a plurality of sample marker position datasets that each represent a position of the respective marker, averaging the plurality of sample marker position datasets and using the average as a marker position in the marker device position dataset if a standard deviation of the sample marker position datasets for each marker is below a predetermined position threshold. 
     
     
         12 . The method according to  claim 1 , wherein:
 a plurality of sample second marker device position datasets are acquired;   a plurality of sample marker device displacement datasets are calculated, which each represent the displacement of the marker device between the first marker device position dataset and a corresponding sample second marker device position dataset of the plurality of sample second marker device position datasets;   the plurality of sample marker device displacement datasets are averaged; and   the average of the plurality of sample marker device displacement datasets is used as the marker device displacement dataset if a standard deviation of the plurality of sample marker device displacement datasets is below a predetermined displacement threshold.   
     
     
         13 . The method according to  claim 1 , wherein:
 marker device displacement datasets are calculated for two different marker devices;   at least one axis of rotation is calculated for each marker device; and   the marker devices are determined to have not rotated about their respective mounts if for each axis of rotation of the first marker device a corresponding axis of rotation of the second marker device is at a distance which is below a predetermined axis divergence threshold.   
     
     
         14 . A non-transitory computer readable storage device storing a computer program which, when running on a computer or when loaded onto the computer, causes the computer to:
 acquire, via a tracking device operably associated with the computer, a first marker device position dataset that represents a position of the marker device before a movement of the marker device;   acquire, via the tracking device, a second marker device position dataset that represents the position of the marker device after the movement of the marker device;   calculate a marker device displacement dataset from the first and second marker device position datasets, the marker device displacement dataset representing the displacement of the marker device;   calculate at least one axis of rotation of the marker device displacement dataset, the calculated at least one axis of rotation including a position of the at least one axis of rotation;   determine whether or not the marker device is rotated about its mount based on the position of the at least one axis of rotation relative to the marker device; and   outputting indication information to an associated user when the computer has determined that the marker device has rotated about its mount, the indication information informing the associated user that the marker device has rotated about its mount.   
     
     
         15 . A data processing method for determining rotation by a marker device of a medical tracking system about its mount, comprising:
 acquiring, by a tracking device, a first marker device position dataset that represents a position of the marker device before a movement of the marker device;   acquiring, by the tracking device, a second marker device position dataset that represents the position of the marker device after the movement of the marker device;   calculating, by a computer operably associated with the tracking device, a marker device displacement dataset from the first and the second marker device position datasets, the marker device displacement dataset representing the displacement of the marker device;   calculating, by the computer, Euler angles of the marker device displacement matrix;   determining, by the computer, that at least one of the Euler angles is larger than a predetermined minimum angle threshold;   calculating, by the computer, at least one axis of rotation of the marker device displacement dataset, the calculated at least one axis of rotation including a position of the at least one axis of rotation;   determining, by the computer, whether or not the marker device is rotated about its mount based on the position of the at least one axis of rotation relative to the marker device; and   outputting indication information to an associated user when the computer has determined that the marker device has rotated about its mount, the indication information informing the associated user that the marker device has rotated about its mount.